# z80:Opcodes:CP

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Jump to navigationJump to searchCP is a subtraction from A that doesn't update A, only the flags it would have set/reset if it really was subtracted.

## Syntax

CP op8

op8 is any one of the allowed inputs.

**Allowed instructions**

cp a cp b cp c cp d cp e cp h cp l cp ixh cp ixl cp iyh cp iyl cp (ix+n) cp (iy+n) cp n ;8 bit constant

## Effects

C, S, and Z flags modified by definition P/V detects overflow

## Uses

Here are some general rules on using CP

### Unsigned

If A == N, then Z flag is set. If A != N, then Z flag is reset. If A < N, then C flag is set. If A >= N, then C flag is reset.

### Signed

If A == N, then Z flag is set. If A != N, then Z flag is reset. If A < N, then S and P/V are different. A >= N, then S and P/V are the same.

## T-States

r denotes 8-bit register.

r | 4 |

X | 7 |

(hl) | 7 |

(ix+X) | 19 |

(iy+X) | 19 |

## See also

BIT,CALL,CPD,CPDR,CPI,CPIR,JP,JR,RET